linux/drivers/clocksource/dw_apb_timer_of.c
Jisheng Zhang 9115df89d1 clocksource/drivers/dw_apb_timer_of: Implement ARM delay timer
Implement an ARM delay timer to be used for udelay(). This allows us to
skip the delay loop calibration at boot on Marvell BG2, BG2Q, BG2CD
platforms. And after this patch, udelay() will be unaffected by CPU
frequency changes.

Note: Although in case there are several possible delay timers, we may
not select the "best" delay timer. Take one Marvell Berlin platform for
example: we have arch timer and dw-apb timer. The arch timer freq is
25MHZ while the dw-apb timer freq is 100MHZ, current selection would
choose the dw-apb timer. But the dw apb timer is on the APB bus while
arch timer sits in CPU, the cost of accessing the apb timer is higher
than the arch timer. We could introduce "rating" concept to delay
timer, but this approach "brings a lot of complexity and workarounds
in the code for a small benefit" as pointed out by Daniel.

Later, Arnd pointed out "However, we could argue that this actually
doesn't matter at all, because the entire point of the ndelay()/
udelay()/mdelay() functions is to waste CPU cycles doing not much at
all, so we can just as well waste them reading the timer register
than spinning on the CPU reading the arch timer more often.", so we
just simply register the dw apb base delay timer.

Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
2015-12-15 09:42:00 +01:00

172 lines
4.4 KiB
C

/*
* Copyright (C) 2012 Altera Corporation
* Copyright (c) 2011 Picochip Ltd., Jamie Iles
*
* Modified from mach-picoxcell/time.c
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <linux/delay.h>
#include <linux/dw_apb_timer.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_irq.h>
#include <linux/clk.h>
#include <linux/sched_clock.h>
static void __init timer_get_base_and_rate(struct device_node *np,
void __iomem **base, u32 *rate)
{
struct clk *timer_clk;
struct clk *pclk;
*base = of_iomap(np, 0);
if (!*base)
panic("Unable to map regs for %s", np->name);
/*
* Not all implementations use a periphal clock, so don't panic
* if it's not present
*/
pclk = of_clk_get_by_name(np, "pclk");
if (!IS_ERR(pclk))
if (clk_prepare_enable(pclk))
pr_warn("pclk for %s is present, but could not be activated\n",
np->name);
timer_clk = of_clk_get_by_name(np, "timer");
if (IS_ERR(timer_clk))
goto try_clock_freq;
if (!clk_prepare_enable(timer_clk)) {
*rate = clk_get_rate(timer_clk);
return;
}
try_clock_freq:
if (of_property_read_u32(np, "clock-freq", rate) &&
of_property_read_u32(np, "clock-frequency", rate))
panic("No clock nor clock-frequency property for %s", np->name);
}
static void __init add_clockevent(struct device_node *event_timer)
{
void __iomem *iobase;
struct dw_apb_clock_event_device *ced;
u32 irq, rate;
irq = irq_of_parse_and_map(event_timer, 0);
if (irq == 0)
panic("No IRQ for clock event timer");
timer_get_base_and_rate(event_timer, &iobase, &rate);
ced = dw_apb_clockevent_init(0, event_timer->name, 300, iobase, irq,
rate);
if (!ced)
panic("Unable to initialise clockevent device");
dw_apb_clockevent_register(ced);
}
static void __iomem *sched_io_base;
static u32 sched_rate;
static void __init add_clocksource(struct device_node *source_timer)
{
void __iomem *iobase;
struct dw_apb_clocksource *cs;
u32 rate;
timer_get_base_and_rate(source_timer, &iobase, &rate);
cs = dw_apb_clocksource_init(300, source_timer->name, iobase, rate);
if (!cs)
panic("Unable to initialise clocksource device");
dw_apb_clocksource_start(cs);
dw_apb_clocksource_register(cs);
/*
* Fallback to use the clocksource as sched_clock if no separate
* timer is found. sched_io_base then points to the current_value
* register of the clocksource timer.
*/
sched_io_base = iobase + 0x04;
sched_rate = rate;
}
static u64 notrace read_sched_clock(void)
{
return ~readl_relaxed(sched_io_base);
}
static const struct of_device_id sptimer_ids[] __initconst = {
{ .compatible = "picochip,pc3x2-rtc" },
{ /* Sentinel */ },
};
static void __init init_sched_clock(void)
{
struct device_node *sched_timer;
sched_timer = of_find_matching_node(NULL, sptimer_ids);
if (sched_timer) {
timer_get_base_and_rate(sched_timer, &sched_io_base,
&sched_rate);
of_node_put(sched_timer);
}
sched_clock_register(read_sched_clock, 32, sched_rate);
}
#ifdef CONFIG_ARM
static unsigned long dw_apb_delay_timer_read(void)
{
return ~readl_relaxed(sched_io_base);
}
static struct delay_timer dw_apb_delay_timer = {
.read_current_timer = dw_apb_delay_timer_read,
};
#endif
static int num_called;
static void __init dw_apb_timer_init(struct device_node *timer)
{
switch (num_called) {
case 0:
pr_debug("%s: found clockevent timer\n", __func__);
add_clockevent(timer);
break;
case 1:
pr_debug("%s: found clocksource timer\n", __func__);
add_clocksource(timer);
init_sched_clock();
#ifdef CONFIG_ARM
dw_apb_delay_timer.freq = sched_rate;
register_current_timer_delay(&dw_apb_delay_timer);
#endif
break;
default:
break;
}
num_called++;
}
CLOCKSOURCE_OF_DECLARE(pc3x2_timer, "picochip,pc3x2-timer", dw_apb_timer_init);
CLOCKSOURCE_OF_DECLARE(apb_timer_osc, "snps,dw-apb-timer-osc", dw_apb_timer_init);
CLOCKSOURCE_OF_DECLARE(apb_timer_sp, "snps,dw-apb-timer-sp", dw_apb_timer_init);
CLOCKSOURCE_OF_DECLARE(apb_timer, "snps,dw-apb-timer", dw_apb_timer_init);